Method for controlling the use of a program signal in a broadcast system, and control device for a receiver for carrying out such a method

ABSTRACT

In a method for controlling the use of a program signal in a broadcast system, comprising one or more broadcasters and a number of receivers, at least a part of the receivers can be provided with a storage medium for storing program signals. The program signal comprises content signals of a first and a second type, wherein the second type of content signals is inserted in time slots in the first type of content signals. At least the first type of content signals is scrambled using control words as scrambling keys to obtain a scrambled program signal. The program signal is scrambled using control words as scrambling keys and the scrambled program signal is broadcasted together with entitlement control messages (ECM&#39;s) containing the control words in an encrypted manner using a second key. Decrypting means are provided at each receiver for retrieving the control words from the ECM&#39;s by decrypting the ECM&#39;s, wherein the control words are delivered by the decrypting means for descrambling the program signal. At least a plurality of ECM&#39;s comprises control information to control the decrypting means in such a manner that at least the time slots for second type of content signals are maintained in the first type of content signals.

This application is filed under 35 U.S.C. § 371 as a nationalization ofPCT application Number PCT/EP00/13393, filed Dec. 18, 2000, which claimspriority to European Patent Application EP 99204482.6, filed Dec. 22,1999.

The invention relates to a method for controlling the use of a programsignal in a broadcast system, comprising one or more broadcasters and anumber of receivers, at least a part of the receivers preferably havinga storage medium for storing program signals, wherein the program signalcomprises content signals of a first and a second type, wherein at leastthe first type of content signals is scrambled using control words asscrambling keys to obtain a scrambled program signal and wherein thescrambled program signal is broadcasted together with entitlementcontrol messages (ECM's) containing the control words in an encryptedmanner using a second key, wherein decrypting means are provided at eachreceiver for retrieving the control words from the ECM's by decryptingthe ECM's, and wherein the control words are delivered by the decryptingmeans for descrambling the program signal. The invention further relatesto a control device for a receiver for carrying out such a method,comprising decrypting means for retrieving the control words from ECM'sby decrypting the ECM's, and for delivering decrypted control words fordescrambling a program signal.

Recently audio/video devices has become available, wherein the device isprovided with a storage medium having sufficient storage capacity tostore hours of audio/video programs. With such audio/video devices it ispossible to use a remote editing agent in the receiver to construct abroadcasting station within the device. The remote editing agent causesvideo and/or audio clips to be presented to the viewer in a continuoussequence simulating a broadcast service. The sequence can be determinedby direct user interaction, user settings or intelligent analysis withinthe receiver of the user's behaviour.

In many cases, a program signal includes both content signals (or moregenerally content signals of a first type) and advertisement signals (ormore generally content signals of a second type), wherein sellingadvertisement time slots in the complete program is an important incomesource of the broadcaster. With the availability of audio/video devicesof the above-mentioned type, the remote editing agent can use the userinteraction/profile to select which advertisements should be inserted inthe advertisement slots in the program signal. In this manner abroadcaster can resell the same advertisement slots to many advertisersand the advertisements can be better targeted to the viewers. This wayof tuning advertisement slots to the viewer requires to add data to theprogram signal with flags indicating the insertion points to insertadvertisements in the advertisement slots and data describing the typeof advertisements and programs, respectively. However a program signalwith flags to indicate the advertisement slots is open to use byunauthorized third parties which can reprogram the receivers to use theprogram signal provided by the broadcaster to insert their ownadvertisements or to remove the advertisement slots completely.

The invention aims to provide a method of the above-mentioned type,wherein unauthorized use of a program signal is prevented in anefficient manner.

According to the method of the invention at least a plurality of ECM'scomprises control information to control the decrypting means in such amanner that at least the time slots for second type of content signalsare maintained in the first type of content signals.

In this manner a method is obtained, wherein unauthorised use of theprogram signal is prevented, because the decrypted ECM's provided by thebroadcaster provide control on the use of the signal, in particular onmaintaining the time slots in the first type of content signal.

Preferably, the ECM's comprise first ECM's for the first type of contentsignals and second ECM's for the second type of content signals, whereinat least a plurality of first and second ECM's is provided with controlinformation, wherein the decrypting means checks the control informationand delivers decrypted control words of the first or second ECM's inaccordance with the control information to descramble content signals ofthe first or second type, respectively.

The invention further provides a control device of the above-mentionedtype characterized in that the decrypting means is adapted to check thecontrol information of the decrypted ECM's and to insert a time slot inthe first type of content signals as indicated by the controlinformation.

The invention will be further explained by reference to the drawings, inwhich an embodiment of the method and control device of the inventionare shown by way of example.

FIG. 1 shows in a very schematic manner an embodiment of a controldevice of the invention.

FIG. 2 shows a flow diagram to explain an embodiment of the method ofthe invention.

FIG. 3 shows a flow diagram to explain a second embodiment of the methodof the invention.

It is noted that in the following examples the insertion ofadvertisements into a content signal, such as a show or a film, isdescribed. However the invention generally relates to a method forcontrolling the use of a program signal, wherein the program signalcomprises a first type of content signals, i.e. the show or film or thelike, and a second type of content signals, for example advertisementsignals, wherein the second type of content signals can be inserted intothe first type of content signals under the control of the broadcaster.

In the method described the program signal that is broadcasted isscrambled irrespective whether it is a pay service or a service basedupon advertisement as source of income. The scrambling is carried out ina usual manner according to a conditional access system with a keyhierarchy. It is noted that the structure of the conditional accesssystem and the descrambling/encryption techniques used are not part ofthe present invention. According to the invention, the conditionalaccess system is used to manage the insertion of the advertisements intothe program signal.

The control device shown in FIG. 1 is adapted to operate according to aconditional access system, wherein so-called entitlement controlmessages or ECM's are broadcasted together with the program signal,wherein the ECM's comprise the control words or first keys which areused to scramble the clear program signal. The control words areencrypted using a second key which is available in the control device,in case of the embodiment shown in FIG. 1 in a smart card 1. The smartcard 1 decrypts the ECM's to provide the clear control words to a unit 2for descrambling the scrambled content signal. The output of the unit 2provides the clear audio/video signals. The input to the descramblingunit 2 may be a compressed signal, in which case the unit 2 alsooperates to decompress the signal. The input signals can be retrievedfrom a storage medium 3, for example a hard disk with large capacity, ordirectly from a demodulator/demultiplexer 4. The signals stored on thestorage medium 3 may come from the demodulator/demultiplexer 4. Thispart of the control device is not part of the present invention and willtherefore not be described further.

Both the content program signal and the advertisement signal have theircorresponding ECM's inserted, i.e. content or first ECM's and advert orsecond ECM's, respectively. Although in this embodiment theadvertisement signal is scrambled with advert ECM's, the advertisementsignal may be sent in the clear or scrambled using the control word ofthe last content ECM. This means that it is also possible to use onlyone type of ECM's.

As the program signal is played back the appropriate ECM's are sent tothe smart card and these ECM's are used to control the use of thecomplete program signal. To this end, the content ECM's may carrycontrol information including a content sequence identifier. Thiscontrol information can include information on the content and rules forinsertion of the advertisement signals into the content. These rules mayfor example indicate specific advertisements which should be insertedinto the specific content signal, for example in case the broadcasterhas sold advertisement slots in specific films, shows or the like. Itwill be clear to the skilled person that the storage medium 3 will havestored several types of advertisement signals, so that different controldevices according to FIG. 1 can insert different advertisementsdepending on user settings or analysis of user behaviour. A furtherpossibility as a rule for insertion of different advertisements isinsertion in dependence of the time of the day.

The ECM's of the advertisement signals also may carry controlinformation including a sequence identifier. The control information mayinclude information identifying the advertising material, informationspecifying how many advert ECM's there are in the sequence of ECM's thatdelivers control words for one advertisement and the order of ECM's.Typically, a conditional access system changes the control word everyfew seconds so that with an advertising slot of for example 30 seconds,there may be several ECM's per advertising slot.

The control information may further include timing informationspecifying a delay between ECM's. In this manner fast forwarding of theadvertisements or submission of advert ECM's without actually processingthe content can be prevented. The smart card 1 is provided with a realtime clock and checks the delay specified by the ECM and if this delayhas not passed, the smart card 1 does not accept the next or any otherECM in the sequence before the delay has actually passed. In this mannerthe advertising slot is enforced during the playback of the programsignal.

It is noted that at least a part of the content ECM's may also includetiming information in the control information, in particular in ECM'sjust before and after an advertisement slot to prevent a start of fastforwarding just before the advertisement slot. The sequence identifiersin both types of ECM's are used to signal the smart card 1 a jump to anew point in the program signal.

According to the method of the invention described various rules forinsertion of advertisements can be used.

In an embodiment wherein only one type of ECM's are used, the decryptionof an ECM can be made dependent on the decryption of a previous ECM. Forexample by using the sequence identifier of the ECM's a next ECM is onlyused to obtain the control word if the previous ECM has indeed beenused. Skipping a part of the program, in particular the time slot foradvertisements is prevented in this manner. As an alternative the sameresult can be obtained by providing timing indices within one type ofECM's. The timing information in the ECM's will enforce a break in thenormal program for insertion of the adverts.

FIG. 2 shows an embodiment wherein timing is used to insert theadvertisements into the content program signal. By way of example a slotof one minute of advertisement could be inserted into each five minutesof program content. To this end the control information of the contentECM's carry information to count down until the advertisement insertionslot. In the flow diagram shown in FIG. 2, each ECM extracted from theprogram signal is checked by the smart card on timing information and ifthe time delay is correct, the ECM is checked on whether or not it is anadvert ECM. If it is a content ECM, the content ECM counter isincremented. Depending on the count of the counter, a flag is set toindicate that an advert ECM should be extracted in the next cycles.After outputting the control word to the descrambler 2, a next ECM isextracted. If an advert ECM is detected by the smart card, a counter foradvert ECM's is incremented and the output control word is provided tothe descrambler 2. When the advertisement slots have passed, the ECMflag is reset to content and a next content ECM is extracted. If theadvertisement slot has not yet passed, a next advert ECM is extracted.

As an alternative to the operation shown in the flow diagram of FIG. 2,only the last ECM before the advertisement insertion point could have anindication to instruct the smart card to start an advertisement slot.

During processing advert ECM's, the smart card 1 ensures by checking thetime delay that the delay between ECM's is such that the specifiedadvertisement duration is maintained even if the user tries to fastforward during the advertisement slot.

As mentioned above, in this example, the content ECM's could containcontrol information which indicates that only specific advertisementsshould be inserted into the next advertisement slot. The smart card willthen only allow corresponding advert ECM's to be processed.

It is possible that the user of the control device switches to anotherchannel during the advertisement slot. In order to guarantee that theadvertisement is viewed, the smart card 1 can maintain a log of theprogram that has been watched by retrieving the program signal from thestorage medium 3. When the user returns to that channel, the smart cardenforces that the correct advertisement sequence is watched before thenext part of program content becomes available.

In FIG. 3 a flow diagram of a second embodiment is shown, wherein forboth the content ECM's and the advert ECM's a counter is used, whereinthe control information of the content ECM's indicates a threshold forthe amount of viewing of the program content which must occur before anadvertisement can be inserted. Once the threshold, i.e. a minimum amountof viewing time, has been reached the smart card 1 may be programmedsuch that it waits for an appropriate insertion point or immediatelystops processing content ECM's until a predetermined number of advertECM's are processed.

In this embodiment the control information of the content ECM's may alsoindicate the appropriate insertion point for the advertisement slot. Inthis manner the advertisements are not randomly inserted in the middleof a scene but only at a scene boundary for example. Of course, thecontrol information of the content ECM's may also indicate a maximumvalue of program viewing time and if exceeded, the smart card 1 does notwait until an appropriate insertion point but immediately starts toprocess advert ECM's.

A program signal may include one or more ECM's having a decision rule aspart of the control information, which decision rule provides the userthe possibility to select a viewing mode with a particular entitlementto watch the content without advertisement insertion. This particularentitlement may be subscription, pay per view or the like.

As an alternative it can be guaranteed that an advertisement slot is notdeleted or skipped by providing control information in the last ECM orplurality of ECM's before the advertisement slot indicating the rate atwhich ECM's are allowed to be processed or the delay before the next ECMis allowed to be processed. For example, this control informationinstructs the control device to wait for two minutes before the next ECMcan be processed.

Although in the above embodiments the invention is explained when usingstored content, the invention can be used in the same manner in watchingor listening normal broadcast signals. The advert ECM's can be used tocheck whether the user has not surfed to another channel. If the userdid surf to another channel access to the content of the channel usingthe described control method, can then be denied for a predeterminedperiod for example.

In the above-described embodiments, a control device is used having ahardware smart card for processing the ECM's as in a conventionalconditional access system. According to an embodiment of the inventiondescribed, the function of the smart card regarding processing of ECM'scan be carried out by a software module which is executed in amicroprocessor of the descrambler 2. This software module is provided bythe broadcaster and is downloaded over the air into the descrambler 2and can be changed regularly to prevent unauthorised persons toreprogram the descrambler 2, for example to completely delete theadvertisement slots or to insert there own advertisements.

The invention is not restricted to the above described embodiment andcan be varied in a number of ways within the scope of the followingclaims.

1. A system comprising: a number of receivers, at least some of thereceivers having a storage medium to store program signals, wherein theprogram signals comprise content signals of a first and a second type,wherein the second type of content signals is inserted in time slots inthe first type of content signals, wherein at least the first type ofcontent signals is scrambled using control words serving as first keysfor scrambling to obtain a scrambled program signal and wherein thescrambled program signal is provided together with entitlement controlmessages (ECMs) containing the control words in an encrypted mannerusing a second key, a decryptor provided at each receiver for retrievingthe control words from the ECMs by decrypting the ECMs, and wherein thecontrol words are delivered by the decryptor for descrambling theprogram signal, and wherein at least a plurality of said ECMs containingthe control words in an encrypted manner further comprises controlinformation to control the decryptor in such a manner that the decryptorprocesses ECMs to deliver decrypted control words for descrambling atleast the first type of content signals so as to maintain at least thetime slots for second type of content signals in the first type ofcontent signals during playback of the program signal.
 2. The system ofclaim 1, further including a real time clock operated at the receiverside, wherein the control information of an ECM near the beginning of atime slot for the second type of content signals indicates a delaybefore a next ECM can be decrypted by the decryptor.
 3. The system ofclaim 1, wherein the ECMs comprise a first ECMs for the first type ofcontent signals and a second ECMs for the second type of contentsignals, wherein at least a plurality of the first and the second ECMsare provided with control information, wherein the decryptor checks thecontrol information and delivers the decrypted control words of thefirst or the second ECMs in accordance with the control information todescramble content signals of the first or the second type,respectively.
 4. The system of claim 3, wherein the control informationof said plurality of ECMs comprises timing information, wherein a realtime clock is operated at the receiver side, wherein the decryptorchecks the timing information of each ECM by means of the real timeclock and continues to deliver control words of the ECMs fordescrambling the program signal only if the timing informationcorresponds with the time indication provided by the real time clock. 5.The system of claim 4, wherein a sequence identifier and a minimum delaywhich should pass before a next ECM should be decrypted are comprised inthe control information of said plurality of ECMs as timing information,wherein the decryptor checks the time passed by means of the real timeclock and continues to deliver a next control word only if the timepassed corresponds with the minimum delay.
 6. The system of claim 3,wherein at least a plurality of first ECMs provides control informationfor the decryptor indicating the decryptor to use a plurality of secondECMs, wherein the control information may comprise timing information onthe time period for using first ECMs and on the time period for usingsecond ECMs, and information on the point within the first type ofcontent signals for inserting the second type of content signals.
 7. Thesystem of claim 6, wherein the second type of content signals comprisecontent signals with corresponding ECMs representing various contents,wherein the control information of at least a part of said plurality offirst ECMs comprises selection identifiers to allow only a selectedcontent signal with corresponding ECMs to be used for insertion into thefirst type of content signals as second type of content signals, whereinin particular the selection identifiers select the content signaldepending on the time of the day.
 8. The system of claim 6, wherein thedecryptor forces the receiver to use all second ECMs corresponding tothe time period indicated for using the second ECMs independent of thereceiver being tuned to the corresponding program signal source.
 9. Thesystem of claim 3, wherein an ECM of the first ECMs for the first typeof content signals comprises control information to switch the decryptorto deliver only first ECMs for the first type of content signals if thedecryptor indicates a viewing mode allowing the use of the first contentsignals only.
 10. The system of claim 1, wherein the control informationof the ECMs comprises a sequence identifier including an index number ofthe previous and/or next ECMs, wherein the decryptor checks the indexnumber of a received ECM against the expected index number, wherein thecontrol word is only provided if the index number received matches theexpected index number.
 11. The system of claim 1, wherein the controlinformation of an ECM comprises information on the insertion of thesecond type of content signals in the first type of content signals. 12.The system of claim 1, wherein the ECMs are inserted in the programsignal in syncrhronisation with the change of the control words used toscramble the program signal.
 13. The system of claim 1, wherein thedecrypting means is provided as a software module broadcasted by abroadcaster, wherein the software module is executed in the receivers,wherein the software module is regularly changed by the broadcaster. 14.The system of claim 1, further including a control device for at leastone of the number of receivers for controlling the use of a programsignal comprising a decryptor to retrieve the control words from ECMs bydecrypting the ECMs, and for delivering decrypted control wordsdescrambling a program signal, wherein the decryptor is adapted to checkthe control information of the decrypted ECMs and to insert a time slotin the first type of content signals by processing ECMs to deliverdecrypted control words for descrambling at least the first type ofcontent signals as indicated by the control information.
 15. The systemof claim 14, wherein the decryptor delivers decrypted control words ofthe first or second ECMs in accordance with the control words of thefirst or second ECMs in accordance with the control information todescramble content signals of the first or second type, respectively.16. The system of claim 14, further comprising a real time clock,wherein the decryptor is adapted to check the timing information in thecontrol information of each ECM by means of the real time clock and tocontinue to deliver control words of the ECMs to descramble the programsignal only if the timing information corresponds with the timeindication provided by the real time clock.